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Seismic Reflection 2: Acquisiton, Processing, and Waveform Analysis

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  • qqq
  • In the Gather process, traces from different shot gathers are rearranged as a CMP gathers.
  • At distance from the source, the tops of records commonly have unwanted noise (direct P- and S waves, refraction events distorted by Tnmo corrections), with few or no reflections. Rather than stack this noise together with reflections recorded near the source, a (commonly triangular) region of CMP gather traces are set to zero amplitude, or muted. On the tops of actual seismic reflection profiles, including many of those in chapter 6, can be see as V-shaped “valleys” in regions where only far offsets comprise the stack traces.
  • Transcript

    • 1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Seismic Reflection 3: Acquisiton, Processing, and Waveform Analysis Introduction to Geophysics-KFUPM
    • 2. Shaybah Field: Data Acquisition Introduction to Geophysics-KFUPM Alfaraj et al., 1998, GeoArabia, Vol. 3, No 2 .
    • 3.
      • Over 120 million seismic traces , covering an area of about 1,100 sq km, were recorded with over 100,000 shot points .
      • Processing of the data was carried out in-house by Saudi Aramco and lasted about 18 months .
      Example from Shaybah Field: Data Acquisition and Processing Introduction to Geophysics-KFUPM Alfaraj et al., 1998, GeoArabia, Vol. 3, No 2.
    • 4. Previous Lecture
      • Snell's Law
      • Reflection "Presentation"
      • Multifold Reflections
      • Receiver Arrays
      • CMP method
      • Processing
      • Normal Move out
      Mid-Term Exam: May 3, Class Time Introduction to Geophysics-KFUPM Field-Trip: April 22, April 24 or April 26, 12.30 AM
    • 5. Resulted from energy that undergoes only one reflection before returning to the surface Primary Reflection Introduction to Geophysics-KFUPM
    • 6. Multiples Reflected energy back up again following a reflection back down at the surface. Introduction to Geophysics-KFUPM
    • 7. Introduction to Geophysics-KFUPM Comparison
    • 8. Introduction to Geophysics-KFUPM Gather
    • 9. NMO – Normal Moveout Correction V Function of X, H (T o ), V Introduction to Geophysics-KFUPM X H
    • 10. NMO – Normal Moveout Correction = t f -t 0 Where t f = two-way time of event at offset distance of x t 0 = two-way time of event at zero-offset X Introduction to Geophysics-KFUPM t f t 0
    • 11. Velocity Analysis = t f -t 0 Know x from geometry & t 0 measured from seismic trace Select a variety of V’s to get best  T Introduction to Geophysics-KFUPM
    • 12. Introduction to Geophysics-KFUPM Velocity Analysis Overcorrected by too slow velocity
    • 13. Introduction to Geophysics-KFUPM Velocity Analysis Under corrected by too fast velocity
    • 14. Introduction to Geophysics-KFUPM Velocity Analysis NMO – Normal Moveout Correction Now Corrected
    • 15. Introduction to Geophysics-KFUPM
    • 16. correct V NMO is one which flattens the reflection hyperbola Introduction to Geophysics-KFUPM Uncorrected CMP gather Correct velocity (224 m/s) Overcorrection: velocity too low (2000 m/s) Undercorrection: velocity too high (2500 m/s)
    • 17. Introduction to Geophysics-KFUPM Gathers and NMO Corrected CMP
    • 18. Introduction to Geophysics-KFUPM NMO Corrections
    • 19. Introduction to Geophysics-KFUPM Mute
    • 20. Introduction to Geophysics-KFUPM Static Corrections SC= (h S3 + h R5 )V E V E : Assumed velocity of the material above

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